The modern railway consists of steel rails secured on top of railway sleepers or cross-ties. The conventional material for cross-ties is wood. When wooden cross-ties are employed, tie plates are used distribute the load and to secure the steel rails to the cross-ties. The tie plates are made of either cast or forged steel and comprise a generally flat steel plate with a substantially flat bottom, a plurality of spike or lag holes located on opposite side ends of the plate, and an upper surface having a pair of parallel, vertically projecting rail securing ribs which define a cradle area or rail seat there between in which the rail is placed. The tie plate upper surface in the rail bearing area is slightly angled to provide an inwardly canted rail seat, with more mass located on the field side of the plate to compensate for the force distribution of the load associated with a train moving along the rail and counteract cross-tie bending moment caused thereby. The rail is secured to the tie plate and cross-tie by various fasteners including spikes and clips intended for that purpose.
Due to normal wear and tear, from time to time railways require regular maintenance and reconditioning to ensure, among other things, that the proper gauge spacing between the steel rails is maintained. Wide gauge can be caused over time by wear to the steel rails. When rails are to be replaced because of wear or otherwise, they are typically replaced one side at a time in quarter mile long sections known as strings. The cross-ties are then resurfaced, or adzed, and the rail bed (i.e. the surface of the cross-ties in the rail bearing area) is refurbished. Before the rail bearing area of the cross-tie can be resurfaced, the associated spikes and tie plates must first be removed. Similarly, prior to new rails being laid, replacement or recycled tie plates must be accurately positioned back upon the ties.
Tie plate replacement is a labor-intensive and cumbersome process. This is due to the significant weight of the individual plates (between about 20-35 lbs. each), the number of tie plates laid in any one section of track being refurbished (wooden cross-ties are placed at 19.5 inch on center intervals, nominally), and the rapid rate at which the tie plates must be manually positioned to keep up with the other operations of track reconditioning, the majority of which are automated. If the tie plates are to be reused, typically each individual tie plate is manually removed from its working position on the cross-tie in the rail bearing area and transferred to either side of the track (usually the field side). This is conventionally accomplished by one or more workers walking along the track with hooks or other manual devices designed for such purpose. Thereafter, once the cross-ties have been adzed, or resurfaced, a worker then must retrieve the steel tie plates individually and properly orient each tie plate for setting upon the upper surface of a cross-tie to form new rail beds. Accurate tie plate placement is critical, and there is not much room for error. Accordingly, reconditioning even a small section of a railway equates to a worker manually moving several tons of weight both out and back into the tie plate's working position after the requisite adzing, resurfacing and other related work to the cross-ties has been completed.
Often times, existing tie plates are replaced with new plates. In this case, prior to the rail changing process; a gondola car having a large electromagnet is used to distribute piles of a dozen or more tie plates at regular intervals along side of the track. Thereafter, workers manually stage the new tie plates next to each of the cross-ties. Once the rail has been cut and fasteners removed, the worn rail is removed via a work crane (also known as a speed swing) which is also equipped with an electromagnet that magnetically collects the old tie plates from the track and deposits them in piles next to the track for collection. The cross-ties are then resurfaced, the new plates are manually positioned and the replacement rail is placed. Once all of the components are properly aligned, the new plates and rail are secured to the cross-ties.
Regardless of whether the tie plates are reused or replaced, railway maintenance requires that a significant number of steel tie plates are moved manually by one or more workers. Considering the relatively rapid rates of placement required, as well as the degree of accuracy required, operator effort and safety become major concerns.